Background: Social phobia is a widespread mental disorder in the general population. Cognitive-behavioral therapy is the most thoroughly studied nonpharmacologic approach in this anxiety disorder. Objectives: The aim of this study is to assess the effectiveness of cognitive-behavioral group therapy in patients with generalized social phobia. Methods: Thirty one patients with diagnosis of generalized social phobia were randomly allocated in two groups. One group of cognitive-behavioral group therapy – CBGT (n = 15) and one Waiting List control group – WL (n = 16). The patients completed four rating scales (Social Phobia Inventory, Fear of Negative Evaluation Scale, Beck Anxiety Inventory and Clinical Global Impression Scale) in the weeks 1 and 12. Results: In all rating scales in the week 12 of treatment, the CBGT patients were rated as more improved than WL. Discussion: In this randomized single-blind clinical trial, the cognitive-behavioral group therapy was superior to Waiting List in the treatment of generalized social phobia.